The material presented as background information in this section of the specification is not necessarily prior art.
Assemblies of lithium-ion battery cells are finding increasing applications in providing motive power in automotive vehicles, aerospace applications, consumer electronics, and in many other commercial applications requiring low weight, highly-efficient electrical power sources. Lithium-sulfur cells, lithium-air cells, sodium-sulfur cells, and other lithium electrode cells, utilized with anhydrous electrolytes, and capacitors of like electrode combinations, are also candidates as a power source for commercial applications requiring an efficient, high power density, electrical power source.
Such electrical power-producing devices typically employ particles of active anode and cathode materials that enable lithium ions or sodium ions to be transported in an anhydrous liquid electrolyte between the electrodes.
For example, each cell of a lithium-ion battery is capable of providing an electrical potential of about three to four volts and a direct electrical current based on the composition and mass of the electrode materials in the cell. The cell is capable of being discharged and re-charged over many cycles. A battery is assembled for an application by combining a suitable number of individual cells in a combination of electrical parallel and series connections to satisfy voltage and current requirements for a specified electric motor or other application. In a lithium-ion battery application for an electrically powered vehicle, the assembled battery may, for example, comprise up to three hundred packaged cells that are electrically interconnected to provide forty to four hundred volts and sufficient electrical power to an electrical traction motor to drive a vehicle. The direct current produced by the battery may be converted into an alternating current for more efficient motor operation.
The batteries may be used, for example, as the sole motive power source for electric motor-driven electric vehicles or as a contributing power source in various types of hybrid vehicles, powered by a combination of an electric motor(s) and a hydrocarbon-fueled engine.
In these automotive applications, each lithium-ion cell typically comprises a negative electrode layer (anode, during cell discharge), a positive electrode layer (cathode, during cell discharge), a thin porous separator layer interposed in face-to-face contact between parallel facing electrode layers, and a lithium-containing, anhydrous liquid, electrolyte solution filling the pores of the separator and contacting the facing surfaces of the electrode layers for transport of lithium ions during repeated cell discharging and re-charging cycles. Each electrode is prepared to contain a porous layer of an electrode material, typically deposited on a major surface of a thin layer of a metallic current collector.
For example, the negative electrode material has been formed by depositing a thin layer of polymer resin-bonded graphite or lithium titanate (LTO) particles, often mixed with conductive carbon black, onto one or both sides of a thin metal foil (an aluminum foil for LTO electrode particles) which serves as the current collector for the negative electrode. The positive electrode also comprises a thin layer of resin-bonded, porous particulate, lithium-metal-oxide composition bonded to a thin aluminum foil which serves as the current collector for the positive electrode. Thus, the respective electrodes have been made by dispersing mixtures of the respective binders and active particulate materials in a suitable solvent or dispersing liquid, depositing the liquid-particulate solid mixture as a layer of controlled thickness on the surface of a current collector foil, and drying, pressing, and fixing the resin-bonded electrode particles to their respective current collector surfaces. The positive and negative electrodes may be formed on current collector sheets of a suitable area and shape, and cut (if necessary) and folded, rolled, or otherwise shaped for assembly into lithium-ion cell containers with suitable porous separators and a non-aqueous liquid electrolyte.
Other electrochemical cell and capacitor combinations may be organized and prepared in an analogous manner as the lithium-ion cells.
In many of these electrochemical cells the electrolyte is a halogen-containing compound that may release fluorine, chlorine, or other unwanted acidic material that can harm the chemical function of the particulate electrode materials. There is a need for a simple and low-cost practice for protecting the electrode particles from harm resulting from the release of an un-wanted acidic substance in the repeated charge-discharge operating cycles of the battery or capacitor, in high temperature storage of the device, or by reaction of incidental or intruding water at any time with the electrolyte salt.